The Xisha Islands are a group of about 40 islets, sandbanks and reefs, and researchers said in ancient times many Chinese merchant ships struck the reefs and sank while on their way to Southeast Asia, India and the Middle East.

Treasures and cultural relics from the wrecks are abundant in the area, archaeologists said.

Illegal salvaging of underwater cultural relics in the South China Sea has been rampant, researchers said, and traces left by thieves in some relic sites show large-scale thefts have occurred this year.